The present invention relates to electronic apparatus, and particularly to prevention of dew condensation on the semiconductor devices within electronic apparatus.
The electronic computer, or so-called computer can be roughly classified into three groups: personal computer for private use, work station for technical computation and relatively small-scale database management, and large general-purpose computer for management of large-scale database such as customer data in banks and telephone companies. The semiconductor devices incorporated in these computers are cooled in various ways. Some personal computers employ natural convective air cooling without use of fans. The other personal computers, work stations and most large computers generally use forced convective air cooling in order for the heat generating devices. However, high-performance large computers use a liquid-circulation cooling systems.
The present invention is based on the results of examination about the liquid cooling in large computers. In recent years, the amount of information of database which the large computer handles increases year by year, while speeding up of services and supply of much information have been requested. In order to meet these demands, it is necessary to improve the processing ability of the central processing unit of the large computer that handles enormous amount of data. However, when the processing ability is improved, the semiconductors in the central processing unit increase the amount of heat generation. Thus, the semiconductor devices are forced to be cooled by a liquid such as water. Recently, electronic apparatus using CMOS device have been widely used.
The CMOS device can increase the operation speed as the temperature decreases, and thus it is required to be cooled to a low temperature. For example, it should be cooled by the refrigerator unit that is used in an air conditioner. However, in order to cool the CMOS chip to 10.degree. C., it is necessary that the refrigerator unit be operated to cool at a temperature as low as, for example, 0.degree. C. Cooling at a low temperature will cause condensation of dew on the peripheral equipment around the semiconductor modules kept at low temperatures.
There is a known electronic-equipment cooler for cooling semiconductor packages or semiconductor modules by use of a refrigerator unit, as disclosed in, for example, JP-A-1-236699. In this prior art, a sealed-up box is provided in which the semiconductor module is placed, and a dehumidifier unit and heater unit are connected to this box. In addition, JP-A-6-119083 discloses another structure having a heat-insulated small chamber in which a refrigerator unit and CPU board are mounted. When this CPU board is changed by another one, the temperature within the chamber is raised to prevent the condensation by a heater enclosed in the single chamber. This heater constitutes a cooling unit, and controls the air within the chamber not to form dew. Moreover, JP-A-5-152779 describes still another structure in which electric resistors that generate heat by current are printed on a circuit board in order to raise the temperature of the circuit board over the dew point temperature by the heat generation.
The electronic apparatus has a cooler for cooling the semiconductor package or semiconductor module by a refrigerator unit, therefore the semiconductor chips can be kept at a low temperature. However, when the temperature of the package or module is different from that of the air surrounding it, dew condenses on it. The semiconductor chips themselves do not cause dew condensation because they are incorporated within a sealed space with inert gas enclosed. However, the semiconductor package or semiconductor module has pins mounted for input and output of data, and thus condensation of dew on these pins will generate serious problems such as short-circuits, signal transmission failure and corrosion. Even if dew does not condense on the pins themselves, dew condensing on other portions of the package or module may drip to become contact with the pins.
Two methods of preventing the condensation can be considered. The first method is to control the state of air around the semiconductor package or module to lower the dew point temperature as described in the prior arts (JPA No. 1-236699, and JPA No. 6-119083). The second method is to control the surface temperature of the semiconductor package or module to rise over the dew point temperature as disclosed in JPA No. 5-152779. The first method, however, requires an apparatus for controlling the humidity of air within an airtight chamber that houses all the semiconductor package or module and the printed wiring board with these package or module mounted.
The second method is to raise the temperature of the whole circuit board over the dew point temperature, but does not consider to keep the semiconductor devices at a low temperature. Moreover, a third method can be used in which a heat-insulating material is provided around the semiconductor package or module. However, when the semiconductor package or module is of multi-chip type, a great number of pins must be provided on the entire surface of the input/output pin side of the multilayered wiring board. Thus, there is not space to mount the heat-insulating material on that large number of pins. Also, it is difficult to mount the condensation preventing means such as a heater.